1. Field of the Invention
The present invention relates to a shock suppressing apparatus and method for a shoulder fired rocket launcher.
2. Discussion of Related Art
A typical shoulder fired rocket launcher comprises an elongated tube which, in its firing position, is placed on the shoulder of the operator, with the forward end through which the rocket is discharged being positioned several feet forward of the operators's head, and with the rear end being a short distance rearwardly of the operator's head. The rocket itself is located in the rear end of the launch tube, and the rocket nozzle is closed by a plug. Upon ignition, there is a very rapid pressure build-up in the rocket propellant chamber, and at a predetermined design pressure level, the nozzle plug is expelled from the nozzle rearwardly at a high velocity, generally in the supersonic range. The rocket is then propelled forwardly through the tube toward its intended target, with the exhaust of the rocket being emitted outwardly from the rear end of the launch tube.
Recent developments in shoulder fired rocket propelled weapons have produced systems that release energy levels in the crew areas that create increased hearing loss hazards. The firing of one of these weapons generally creates a peak noise pulse that can exceed 180 decibels at the gunner's position. In this environment, the gunner is required to wear earplugs or earmuffs or possibly both. Even with this protection, gunners may suffer major temporary or permanent hearing loss problems that could degrade their effectiveness in performing regular duties. Also, the flash and smoke produced by one of these weapons gives away the gunner position and makes it vulnerable to return fire.
Attempts to solve the problem have been concentrated on tailoring the propulsion system to minimize peak noise levels. As discussed above, most small rocket engines have a plug in the throat of the nozzle to allow the chamber pressure to build up to a required level before firing, at which time the plug is expelled. The plug velocity after expulsion is supersonic and creates a shock wave for a short distance after it leaves the rocket nozzle. The shock wave created by the plug has been found to be a minor source of rocket engine noise. The major peak noise source is the initial pulse of rapidly expanding high pressure exhaust gasses issuing from the rocket propellant chamber, through the nozzle and into the atmosphere just after the plug is expelled. To reduce the peak noise level, considerable research has been conducted to optimize the pressure level and propellant burn time reached before the plug is expelled. Research has been successful in varying these parameters, however, it has not been successful in reducing the noise level to any significant extent. A further attempt to reduce the noise level is based on energy conservation. This technique is illustrated by the "Armbrust Weapons System." The basic technique is both to perform mechanical work and to contain the gases generated by the firing inside a pressure vessel. In this system, both the missile and an inert mass are enclosed in a pressure chamber of a launch tube, with the motor being placed between the missile and the inert mass. When the weapon is fired, the missile and the inert mass move in opposite directions to minimize recoil, and the motor exhaust products are trapped inside the pressure chamber. The gases are released over a relatively long period of time with the noise being reduced by trapping the exhaust gases and releasing them over a long period of time.
While the approach used in the Armbrust System is effective in sound reduction, it has several severe drawbacks. It is heavy since the missile and the inert mass must have the same mass and the pressure chamber must be strong enough to hold the motor exhaust products. Thus, this apparatus is approximately twice as heavy as a conventional rocket system. Also, it is expensive to fabricate.
Another attempt to reduce the noise generated by a shoulder-fired rocket is disclosed in U.S. Pat. No. 4,203,347 issued to Pinson et al. The Pinson system uses a transient shock suppressor attached to the aft end of the launcher. The suppressor comprises a circumferential housing structure having a longitudinal axis and a forward end adapted to be mounted to the rear of a launch tube so that the longitudinal axis is in general alignment with the longitudinal axis of the launch tube. The housing structure is made from metal and mounts a plurality of baffles which extend radially inward from the housing toward the longitudinal axis of the housing. The baffles define a longitudinally aligned opening which permits rearward ejection of a nozzle plug from a rocket mounted in the launch tube and permits rearward discharge of gaseous exhaust from the rocket. The Pinson et al suppressor permits expansion of the gases coming from the rocket nozzle to near atmospheric pressure through a series of expansion chambers bounded by the baffles and the housing structure. The pressure levels reached in these chambers are very high and create the requirement for a heavy structural housing and baffles. This controlled expansion reduces the energy of the sound pressure wave emitted from the system and moves the noise emitter further away from the gunner's ear position. This design reduces the noise level at the gunner's position, however, the suppressor which is inherently heavy acts as a secondary nozzle which may propel the launcher downrange. Also, the suppressor of Pinson et al has little effect on suppressing the flash and smoke produced by the rocket.
U.S. Pat. No. 3,745,876 issued to Rocha discloses a telescoping ammunition launcher comprising two or more flash and blast deflector sections which may be telescoped into a small size and may be attached to the firing tube of a firearm. No mention is made in the Rocha disclosure concerning noise suppression, and it does not appear that the Rocha device was designed to be used as a noise suppressor.